Apparatus for the washing of primarily, cellulosic pulp

ABSTRACT

In the liquid treatment of cellulosic pulp by a procedure comprising passing a column of a slurry of the pulp to be treated through a cylindrical vessel, in one direction, and forcing a treating liquid through the column, in a direction transverse to the major axis of the column, from a delivery space for such treating liquid toward a collection vessel for used treating liquid, said collection vessel having a pervious wall immediately adjacent said column on that side thereof remote from said delivery space, it is desirable-in the interest of preventing clogging of the pervious wall-intermittently to interrupt inflow of liquid into said vessel by pressure variations induced by a gaseous fluid discharged under pressure adjacent said pervious wall.

United States Patent Pettersson APPARATUS FOR THE WASHING OF PRIMARILY, CELLULOSIC PULP Division of Ser. No. 850,923, Aug. 18, 1969.

Foreign Application Priority Data Sept. 18, 1968 Sweden 1 2572/68 US. Cl. ..68/l8l R, 68/183 Int. Cl ..D2lc 7/00 Field of Search ..68/l 81 R, 183

July 18, 1972 Primary Examiner-William l. Price AnorneyPierce, Seheffler & Parker 57 ABSTRACT In the liquid treatment of cellulosic pulp by a procedure comprising passing a column of a slurry of the pulp to be treated through a cylindrical vessel, in one direction, and forcing a treating liquid through the column, in a direction transverse to the major axis of the column, from a delivery space for such treating liquid toward a collection vessel for used treating liquid, said collection vessel having a pervious wall immediately adjacent said column on that side thereof remote from said delivery space, it is desirable-in the interest of preventing clogging of the pervious wall-intermittently to interrupt inflow of liquid into said vessel by pressure variations induced by a gaseous fluid discharged under pressure adjacent said pervious wall.

4 Claims, 3 Drawing Figures 5 1 3 7 53;; 20 .15 E 5 3 $55 L5? 31 111315 10' "1 5:31 F 11 3i ll\ 11.

PATENIED JUL 1 8 m2 FIG'.3'

APPARATUS FOR THE WASHING OF PRIMARILY, CELLULOSIC PULP This application is a division of my co-pending application, Ser. No. 850,923 filed Aug. 18, 1969.

Co-pending U.S. Pat. application, Ser. No. 720,717, (now U.S. Pat. 3,622,262) filed Apr. 11, 1968 by Nils Gustav Leffler and assigned to Sunds Aktiebolag, Sundsvall, Sweden, relates to a method of and/or apparatus for the liquid treatment, primarily, for the washing (but also for the displacement and dewatering) of material, primarily fibrous material, suspended in a liquid and fed through a preferably upright container of suitably cylindrical shape in the axial direction of said container, said treatment being carried out in that part of the container which is filled with the material, the treatment liquid being caused to flow through the suspension of material from at least one supply means for the treatment liquid toward at least one collecting means for withdrawn liquid, said collecting chamber having a pervious wall. In the method in question the influx of the withdrawn liquid into the collecting chambers is interrupted, entirely or partly, at suitable intervals, in order to prevent clogging of the pervious walls of the collecting chambers and/or to facilitate the travel of material past or along said surfaces. In that connection it has been proposed to generate the pressure variations, resulting from said pulsating flow, through the intermediary of a liquid, primarily water, which by means of a vibrator or some other means generates pulsations within the liquid.

It has now been found that, in accordance with an advantageous, further development of the above-described way of proceeding, it is possible to use a gas, for instance air, as the medium for transmitting the pressure variations. A considerable advantage of using, for instance, air as the medium for transmitting the pressure variations consists therein that the acceleration forces, acting on the impulse medium, will be of an entirely different order than if using, for instance, water because the volumetric weight of air at an atmospheric pressure of l and at a temperature of C. amounts to only about 1/800 of the volumetric weight of water. Furthermore, because of the lower density of the impulse medium (gas, air) and/or the longer time of impulse that can be used (the time factor is not critical at the impulsation), a more uniform distribution of pressure is obtained. Finally, a higher speed of reflux and a higher effective speed of drainage of the washing liquid can be obtained.

The invention will be explained in greater detail in the following description, reference being had therein to the accompanying drawing, in which FIG. 1 shows a vertical sectional view of part of an apparatus suitable for the practical use of the invention, the apparatus being connected to an upright container for the treatment of fibrous material;

FlG. 2 is a vertical sectional view on an enlarged scale, showing that part of the device which is located next to the gas- (air-) pulsator; and

FIG. 3 shows, in a vertical sectional view and on an enlarged scale, a modified embodiment of supplying gas to the outside of a collecting chamber for withdrawn liquid.

Numeral 1 indicates part of the upper portion of an upright, preferably cylindrical container, adapted to be continuously traversed by material to be treated, preferably cellulosic pulp 2, in the direction indicated by the arrows A. The entire room for introducing the treatment (washing) liquid is indicated by 3 and numeral 4 indicates a surface skimming means of a known kind stationarily mounted on a rotary shaft 5. Numerals 6, 7 and 8 indicate supply chambers for washing liquid, which chambers may be stationarily and/or rotatably mounted. Also they may be embodied in a known manner, for instance as substantially vertically extending spray pipes or nozzles, which are movable along paths concentric with annular collecting chambers for withdrawn liquid in accordance with the disclosure of the U.S. Pat. No. 3,372,087. Numerals 9 and 10 indicate collecting chambers for withdrawn liquid, said chambers being preferabl devised as hollow annular sieves. With the collecting cham ers 9 and 10 there communicate one or more pipes 11 for leading away the withdrawn liquid by way of an overflow 12. With the collecting chambers 9 and 10 there also communicate at least one pipe 13, which is connected to a means for generating pressure variations by means of a gas, primarily air. The means in question comprises a container 14, to which gas (air) is to be supplied. Within the pipe 13 there is provided a solenoid valve 15, controlled by, for instance, a time relay. Said time relay alternately connects the collection chambers with the pressure container 14 and with the atmosphere, respectively. The generated pressure variations produce a pulsating flow of gas (air) and/or liquid through the slots or holes 16 in the walls of the collecting chambers 9 and 10, corresponding to the pulsating flow of liquid in the apparatus according to the aforementioned copending application, Ser. No. 720,717, Leffler, which facilitates the flowing of the withdrawn liquid (indicated by arrows B). The limits of the level of liquid in the sieve is marked in FIG. 2 by a double arrow C. Numeral 19 indicates a supply pipe for leading washing liquid to the chamber 8. As will appear from the just-mentioned co-pending application there are corresponding supply pipes leading also to the chambers 6 and 7. Finally treated material (washed pulp) leaves through the outlet 20.

In the modified embodiment according to FIG. 3 the gas (air) is supplied through a pipe 17, provided with slots 18 and positioned at the lower portion of the collecting chamber. In that case the gas (air) is supplied on the outside of the chamber, so that, during the very pressure impulse, said outside is flushed with gas (air). The functioning will then be such that gas (air) will enter between the outside of the chamber and the suspension of material by which clogging of the holes of the sieve will be prevented and at the same time the movement of the suspension will be facilitated.

I claim:

1. An apparatus for liquid treatment of fibrous materials suspended in a liquid comprising an upright container, adapted to be traversed, in its axial direction, by a suspension to be subjected to liquid treatment, at least one means for supplying treatment liquid and at least one chamber for collecting withdrawn liquid, said means and chamber being provided within said container and being positioned within the suspension within said container, said means and chamber being located transversely of the container, means for delivering pressure impulses of a gas to the collecting chamber for withdrawn liquid which delivery means includes at least one conduit connecting the collecting chamber with said means for delivering time-controlled doses of compressed gas and operatively connected to said conduit, said delivery means comprising a container for gas under pressure connected to a time-controlled means.

2. An apparatus according to claim 1, comprising an upright container of substantially cylindrical shape, adapted to be traversed, in its axial direction, by a suspension to be subjected to liquid treatment, at least one means for supplying treatment liquid being provided within said container and being positioned below the intended level of suspension within said container, and at least one chamber for collecting withdrawn liquid, arranged in a corresponding manner but displaced in the radial direction in the container, means for delivering a pulsated flow of a gas under pressure to the collecting chamber for withdrawn liquid which delivery means includes at least one conduit connecting the collecting chambers with said means for delivering time-controlled doses of compressed gas and operatively connected to said conduit.

3. Apparatus according to claim 2 in which said conduit is adapted to deliver gas to the outside of the collecting chamber.

4. Apparatus according to claim 2, in which said conduit debouches into the collecting chambers proper. 

1. An apparatus for liquid treatment of fibrous materials suspended in a liquid comprising an upright container, adapted to be traversed, in its axial direction, by a suspension to be subjected to liquid treatment, at least one means for supplying treatment liquid and at least one chamber for collecting withdrawn liquid, said means and chamber being provided within said container and being positioned within the suspension within said container, said means and chamber being located transversEly of the container, means for delivering pressure impulses of a gas to the collecting chamber for withdrawn liquid which delivery means includes at least one conduit connecting the collecting chamber with said means for delivering time-controlled doses of compressed gas and operatively connected to said conduit, said delivery means comprising a container for gas under pressure connected to a time-controlled means.
 2. An apparatus according to claim 1, comprising an upright container of substantially cylindrical shape, adapted to be traversed, in its axial direction, by a suspension to be subjected to liquid treatment, at least one means for supplying treatment liquid being provided within said container and being positioned below the intended level of suspension within said container, and at least one chamber for collecting withdrawn liquid, arranged in a corresponding manner but displaced in the radial direction in the container, means for delivering a pulsated flow of a gas under pressure to the collecting chamber for withdrawn liquid which delivery means includes at least one conduit connecting the collecting chambers with said means for delivering time-controlled doses of compressed gas and operatively connected to said conduit.
 3. Apparatus according to claim 2 in which said conduit is adapted to deliver gas to the outside of the collecting chamber.
 4. Apparatus according to claim 2, in which said conduit debouches into the collecting chambers proper. 